1,482 research outputs found
Low latency search for Gravitational waves from BH-NS binaries in coincidence with Short Gamma Ray Bursts
We propose a procedure to be used in the search for gravitational waves from
black hole-neutron star coalescing binaries, in coincidence with short
gamma-ray bursts. It is based on two recently proposed semi-analytic fits, one
reproducing the mass of the remnant disk surrounding the black hole which forms
after the merging as a function of some binary parameters, the second relating
the neutron star compactness, i.e. the ratio of mass and radius, with its tidal
deformability. Using a Fisher matrix analysis and the two fits, we assign a
probability that the emitted gravitational signal is associated to the
formation of an accreting disk massive enough to supply the energy needed to
power a short gamma ray burst. This information can be used in low-latency data
analysis to restrict the parameter space searching for gravitational wave
signals in coincidence with short gamma-ray bursts, and to gain information on
the dynamics of the coalescing system and on the internal structure of the
components. In addition, when the binary parameters will be measured with high
accuracy, it will be possible to use this information to trigger the search for
off-axis gamma-ray bursts afterglows.Comment: 5 pages, 1 figure, changes in the introduction and in the concluding
remarks. Accepted for publication in Phys. Rev.
Solving the relativistic inverse stellar problem through gravitational waves observation of binary neutron stars
The LIGO/Virgo collaboration has recently announced the direct detection of
gravitational waves emitted in the coalescence of a neutron star binary. This
discovery allows, for the first time, to set new constraints on the behavior of
matter at supranuclear density, complementary with those coming from
astrophysical observations in the electromagnetic band. In this paper we
demonstrate the feasibility of using gravitational signals to solve the
relativistic inverse stellar problem, i.e. to reconstruct the parameters of the
equation of state (EoS) from measurements of the stellar mass and tidal Love
number. We perform Bayesian inference of mock data, based on different models
of the star internal composition, modeled through piecewise polytropes. Our
analysis shows that the detection of a small number of sources by a network of
advanced interferometers would allow to put accurate bounds on the EoS
parameters, and to perform a model selection among the realistic equations of
state proposed in the literature.Comment: minor changes to match the version published on PR
Constraining the equation of state of nuclear matter with gravitational wave observations: Tidal deformability and tidal disruption
We study how to extract information on the neutron star equation of state
from the gravitational wave signal emitted during the coalescence of a binary
system composed of two neutron stars or a neutron star and a black hole. We use
post-Newtonian templates which include the tidal deformability parameter and,
when tidal disruption occurs before merger, a frequency cut-off. Assuming that
this signal is detected by Advanced LIGO/Virgo or ET, we evaluate the
uncertainties on these parameters using different data analysis strategies
based on the Fisher matrix approach, and on recently obtained analytical fits
of the relevant quantities. We find that the tidal deformability is more
effective than the stellar compactness to discriminate among different possible
equations of state.Comment: 13 pages, 4 figures, 4 tables. Minor changes to match the version
appearing on Phys. Rev.
Rotating proto-neutron stars: spin evolution, maximum mass and I-Love-Q relations
Shortly after its birth in a gravitational collapse, a proto-neutron star
enters in a phase of quasi-stationary evolution characterized by large
gradients of the thermodynamical variables and intense neutrino emission. In
few tens of seconds the gradients smooth out while the star contracts and cools
down, until it becomes a neutron star. In this paper we study this phase of the
proto-neutron star life including rotation, and employing finite temperature
equations of state. We model the evolution of the rotation rate, and determine
the relevant quantities characterizing the star. Our results show that an
isolated neutron star cannot reach, at the end of the evolution, the maximum
values of mass and rotation rate allowed by the zero-temperature equation of
state. Moreover, a mature neutron star evolved in isolation cannot rotate too
rapidly, even if it is born from a proto-neutron star rotating at the
mass-shedding limit. We also show that the I-Love-Q relations are violated in
the first second of life, but they are satisfied as soon as the entropy
gradients smooth out.Comment: 15 pages, 9 figures, 7 tables; minor changes, and extended discussion
on the I-Love-Q relation
Tidal deformations of a spinning compact object
The deformability of a compact object induced by a perturbing tidal field is
encoded in the tidal Love numbers, which depend sensibly on the object's
internal structure. These numbers are known only for static,
spherically-symmetric objects. As a first step to compute the tidal Love
numbers of a spinning compact star, here we extend powerful perturbative
techniques to compute the exterior geometry of a spinning object distorted by
an axisymmetric tidal field to second order in the angular momentum. The spin
of the object introduces couplings between electric and magnetic deformations
and new classes of induced Love numbers emerge. For example, a spinning object
immersed in a quadrupolar, electric tidal field can acquire some induced mass,
spin, quadrupole, octupole and hexadecapole moments to second order in the
spin. The deformations are encoded in a set of inhomogeneous differential
equations which, remarkably, can be solved analytically in vacuum. We discuss
certain subtleties in defining the multipole moments of the central object,
which are due to the difficulty in separating the tidal field from the linear
response of the object in the solution. By extending the standard procedure to
identify the linear response in the static case, we prove analytically that the
Love numbers of a Kerr black hole remain zero to second order in the spin. As a
by-product, we provide the explicit form for a slowly-rotating,
tidally-deformed Kerr black hole to quadratic order in the spin, and discuss
its geodesic and geometrical properties.Comment: 27 pages, 1 figure, 6 appendices; v2: improvements and
clarifications, version to appear in PR
Equation-of-state-independent relations in neutron stars
Neutron stars are extremely relativistic objects which abound in our universe
and yet are poorly understood, due to the high uncertainty on how matter
behaves in the extreme conditions which prevail in the stellar core. It has
recently been pointed out that the moment of inertia I, the Love number lambda
and the spin-induced quadrupole moment Q of an isolated neutron star, are
related through functions which are practically independent of the equation of
state. These surprising universal I-lambda-Q relations pave the way for a
better understanding of neutron stars, most notably via gravitational-wave
emission. Gravitational-wave observations will probe highly-dynamical binaries
and it is important to understand whether the universality of the I-lambda-Q
relations survives strong-field and finite-size effects. We apply a
Post-Newtonian-Affine approach to model tidal deformations in compact binaries
and show that the I-lambda relation depends on the inspiral frequency, but is
insensitive to the equation of state. We provide a fit for the universal
relation, which is valid up to a gravitational wave frequency of ~900 Hz and
accurate to within a few percent. Our results strengthen the universality of
I-lambda-Q relations, and are relevant for gravitational-wave observations with
advanced ground-based interferometers. We also discuss the possibility of using
the Love-compactness relation to measure the neutron-star radius with an
uncertainty of about 10% or smaller from gravitational-wave observations.Comment: 5 pages, 2 figures, 2 table
Constraining modified theories of gravity with gravitational wave stochastic background
The direct discovery of gravitational waves has finally opened a new
observational window on our Universe, suggesting that the population of
coalescing binary black holes is larger than previously expected. These sources
produce an unresolved background of gravitational waves, potentially
observables by ground-based interferometers. In this paper we investigate how
modified theories of gravity, modeled using the ppE formalism, affect the
expected signal, and analyze the detectability of the resulting stochastic
background by current and future ground-based interferometers. We find the
constraints that AdLIGO would be able to set on modified theories, showing that
they may significantly improve the current bounds obtained from astrophysical
observations of binary pulsars.Comment: Results updated to match the version accepted on Phys. Rev. Let
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